Anaerobic fermentor

ABSTRACT

An anaerobic fermentor comprising: a container vessel divided into at least two compartments each having a floor, a roof, and a layer of liquid-pervious packing material disposed horizontally across the compartment at a position intermediate the roof and the floor with its lower surface upwardly spaced from the floor and its upper surface downwardly spaced from the roof; liquid conduits connecting successive compartments in series and connecting the space between the roof and packing layer of one compartment to the space between the floor and packing layer of a succeeding compartment; means for introducing liquid to be treated to the first of the successive compartments; means for removing treated liquid from the last of the successive compartments; means for the removal of gas from the space between the packing layer and the roof of each compartment; and means for the removal of solids from the fermentor.

BACKGROUND OF THE INVENTION

This invention is concerned with improvements in and relating toapparatus for the anaerobic fermentation of organic liquid materials orespecially organic waste materials.

The anaerobic fermentation of organic waste materials is a wellestablished process and has conventionally been carried out in a closedvessel which may be provided with stirring or agitation means. It has,further, been proposed to carry out anaerobic fermentation in a packedvessel, that is a vessel packed with an ordered or random array ofpacking elements such as are used in the chemical enginerring industryin, for example, distillation towers, scrubbers and the like.

SUMMARY OF THE INVENTION

It has now been found, in accordance with the present invention, that alayer of packing material may be used in an anaerobic fermentor not toserve as a medium in which anaerobic fermentation is carried but,rather, as a pervious barrier to define an anaerobic fermentation zone.By using such a layer of packing material it is possible to construct areactor containing two or more anaerobic fermentation zones, thereby toprovide a reactor capable of enhanced capacity.

According to the invention, therefore, there is provided an anaerobicfermentor comprising:

(i) a container vessel divided into at least two compartments eachhaving a floor and a roof, a layer of liquid-pervious packing materialdisposed horizontally across the compartment at a position intermediatethe roof and the floor with its lower surface upwardly spaced from thefloor to define a fermentation zone therebetween and its upper surfacedownwardly spaced from the roof;

(ii) liquid conduits connecting successive compartments in series andconnecting the space between the roof and packing layer of onecompartment to the space between the floor and packing layer of asucceeding compartment;

(iii) means for introducing liquid to be treated into the space betweenthe packing layer and the floor of the first of the successivecompartments; and

(iv) means for removing treated liquid from the space between thepacking layer and roof of the last of the successive compartments.

In operation, the liquid to be treated is introduced, via theappropriate conduit, into the first compartment in the space between thefloor and packing layer of that compartment (the fermentation zone). Theliquid passes upwardly through the packing layer and is then conveyed,by the appropriate conduits, to the space between the floor and packinglayer of the succeeding compartment and then flows upwardly through thepacking layer of that compartment and is thence conveyed downwardly tothe next successive compartment or, in the case of a two compartmentreactor is discharged as treated liquid material.

Generally such compartment will be provided with means for discharginggas evolved during the anaerobic fermentation (typically methane) andsuch means will connect with the space intermediate the upper surface ofthe packing layer and the roof of the compartment. Further, one or morecompartments may be provided with means for discharging solids (sludge)accumulating in the fermentation zone thereof.

The successive compartments of the fermentor in accordance with theinvention may be arranged vertically or horizontally.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be well understood, reference will nowbe made to the accompanying schematic drawings in which:

FIG. 1 is a vertical section through one embodiment of fermentor inaccordance with the invention in which the compartments are arrangedvertically; and

FIG. 2 is a vertical section through a fermentor in accordance with theinvention in which the compartments are arranged horizontally.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1 of the drawings, a reactor in accordance with theinvention comprises a closed containing vessel comprising a generallycylindrical shell 1 having a roof 2 and a floor 3. The containing vesselis divided into three superimposed compartments by means of dividingmembers 4 and 5. Each of dividing members 4 and 5, and the floor 3 ofthe containing vessel are of generally downwardly dished shaped and eachis provided at its centre with a sump 6. Each of the three compartmentsis provided with a layer of packing 7 extending horizontally across thecompartment at a position between the roof and floor of the compartmentand dividing each compartment into two zones, an upper zone (8a, 9a,10a) between the upper surface of the layer of packing and the roof ofthe compartment and a lower zone (8b, 9b, 10b) between the lower surfaceof the packing layer and the floor of the compartment. Downwardlyextending conduits 11 connected the upper zone 8a of the uppermostcompartment with the lower zone 9b of the intermediate compartment and,similarly, vertically extending conduits 12 connect the upper zone 9a ofthe intermediate compartment with the lower zone 10b of the bottomcompartment. A conduit 13, for the introduction of liquid to be treated,connects with the lower zone 8b of the upper compartment and a conduit14, for the removal of treated liquid, connects with the upper zone 10aof the lower compartment.

Gas offtake conduits 15 connect with the upper zones 8a, 9a and 10a ofthe compartments at a position above the upper ends of conduits 11 and12 (in the case of zones 8a and 9a respectively) and above the level ofconduit 14 in the case of zone 10a. Each of sumps 6 is provided with aconduit 16 for removal of solids (sludge) accumulating therein.

In operation, liquid to be treated is introduced via conduit 13 into thelower zone 8b of the upper compartment, passes upwardly through thepacking layer 7 in that compartment and thence downwardly throughconduits 11 into the lower zone 9b of the intermediate compartmentwhence it flows upwardly through the packing layer 7 of that compartmentand thence downwardly through conduits 12 into the lower zone 10b of thelower compartment and finally, having passed through packing layer 7 ofthat zone, is discharged via conduit 14. Gases evolved in the variouscompartments are taken off via conduits 15 and sludge accumulating inthe bottom of the compartments may be discharged via conduits 16.

The fermentor shown in FIG. 2 of the drawings comprises a containingvessel formed of a generally cylindrical shell 1 having a floor 2 and aroof 3. The interior of the containing vessel is divided intocompartments by means of generally vertical divider 17 extendingupwardly from floor 2 to roof 3 of the containing vessel.

Each of the components thus formed is provided with a generallyhorizontal packing layer 7 dividing the compartment into an upper zone(18a, 19a) and a lower zone (18b, 19b) in a manner similar to thatdescribed above in connection with the apparatus shown in FIG. 1. Agenerally vertical conduit 20 connects the upper zone, 18a, of the firstcompartment with the lower zone 19b of the second compartment. A conduit13 for the introduction of liquid to be treated connects with the lowerzone 18b of the first compartment and a conduit 14 for the discharge oftreated liquid connects with the upper zone 19a of the secondcompartment. Each of the upper zones of the compartments is providedwith a gas oftake conduit 15 located, in the case of the firstcompartment above the upper end of conduit 20 and, in the case of thesecond compartment, above liquid discharge conduit 14.

In operation, liquid to be treated is introduced via conduit 13 into thelower zone 18b of the first compartment and thence passes upwardlythrough the packing layer 7 of that compartment into the upper zone 18aand thence, via conduit 20, into the lower zone 19b of the secondcompartment and thence upwardly through the packing layer of thatcompartment into zone 19a and is finally discharged via conduit 14.

An important feature of the apparatus of the invention is, the provisionof a layer of packing in each compartment. This packing may be formed ofan ordered array of packing elements, e.g. perforated plates or verticalor sloped plates, but will more conveniently be formed of a dumped orrandom array of packing elements. So called "dumped" packings possessthe advantage thay they may be simply introduced into the reactionvessel by being dumped therein. Suitable dumped packing elements includeconventional Raschig rings, Pall-type rings and saddle-type packings. Ithas, however, been found that packing elements having an aspect ratio ofless than unity (e.g. less than 0.66, preferably from 0.5 to 0.25) areof particular use in forming the packing array used in the apparatus ofthe invention. Suitable packing elements meeting the required aspectratio criterion include rings which may or may not be provided withapertures in their side walls and internal radial or diametric rings,and so-called "Tellerette" rings (packing elements formed of a torroidalhelix). As will be appreciated, such dumped packing elements should besupported on an appropriate perforated support. Random layers may alsobe formed of "demister" material, e.g. knitted of woven materails suchas knitted or woven metal or plastics filaments.

The fermentation apparatus of the invention may be used to process awide variety of organic waste liquids (by which term is meant aqueoussolutions and/or suspensions of organic waste material) such as domesticsewage liquors, waste from food and beverage producing plants and fromoil refineries.

The fermentation serves two principal functions namely

(a) to reduce the BOD of the waste liquid whilst,

(b) producing useful material such as methane from the waste material.Fermentation carried out in the fermentation apparatus of the inventionmay be carried out under conventional conditions for anaerobicfermentation that is at temperatures of from 20° to 80° C.

I claim:
 1. An anaerobic fermentor comprising(i) a container vesseldivided into at least two compartments each having a floor, a roof, andmeans for dividing the compartment into superposed zones and permittingupward fluid passage between the zones, said dividing and upward fluidpassage means comprising a layer of liquid-pervious packing materialdisposed horizontally across the compartment at a position intermediatethe roof and the floor with its lower surface upwardly spaced from thefloor to define a fermentation zone therebetween and its upper surfacedownwardly spaced from the roof; (ii) liquid conduit means connectingsuccessive compartments in series and providing downward liquid flowfrom the space between the roof and packing layer of one compartment tothe space between the floor and packing layer of a succeedingcompartment; (iii) means for introducing liquid to be treated into thespace between the packing layer and the floor of the first of thesuccessive compartments; (iv) means for removing treated liquid from thespace between the packing layer and roof of the last of the successivecompartments; (v) means provided in at least one fermentation zone fordischarging solids from the fermentor; and (vi) means provided in eachcompartment between the upper surface of the packing layer and the roofof the compartment for discharging gas.